Method of manufacturing impregnated ferrite



March 29, 1960 A. H. IVERSEN METHOD OF MANUFACTURING I MPREGNATED FERRITE Original Filed Aug. 19, 1955 m H 56 w v S E Mr. G e m A V 4. H 0 h r U h M r A 2 3 Y B 5 .0. I F m r lll+ ..llll F mm Mum m M GRE TR MEL mum EFE EFE L L mtmmmu xv United States Patent METHOD OF MANUFACTURING IMPREGNATED FERRITE Arthur H. Iversen, Santa Monica, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware 3 Claims. (Cl. 25-156) This invention relates generally to ferrites for use in microwave applications, and more particularly to a method for manufacturing an impregnated ferrite body.

This application is a division of application Serial Number 529,512, filed August 19, 1955, now Patent No. 2,846,655 entitled Impregnated Ferrite.

A typical ferrite dielectric element for use in microwave devices has the shape of a rod tapered to a point on both ends. Ordinarily, the rod is formed by extrusion, cut to length, and then ground to have pointed ends for impedance matching purposes. The extrusion process is an expensive one requiring elaborate equipment, and due to fabrication difiiculties, produces stress lines within the Patented Mar. 29, 19 60 ice method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawing: v 1 I Fig. 1 is a partially' sectioned view of a typical, conventional ferrite element;

Fig. 2 is a sectional view of a structure illustrating one step of the process of the invention;

Fig. 3 is a partially sectioned view showing one step of an alternative method of the invention;

Fig. 4 is a view of a finished ferrite element in accordance with the present invention; and

Fig. 5 is a pair of graphs to aid in the description of the invention.

Referring now to the drawing, and more particularly to Fig. 1, there is shown a length of extruded ferrite rod 10, the ends of which have been ground to a predeter mined taper for impedance matching purposes. A layer of glass 12 is shown covering the finished ferrite body in a manner to hermetically seal the porous ferrite and to further aid in impedance matching. Potential fissure areas or surfaces 14, as previously pointed out, are caused high temperature or high applied microwave power, the

extruded rod frequently cracks and crumbles. Also, the extruded ferrite body is inherently porous because ferrites are non-vitrified ceramics. Accordingly, when a ferrite is heated, it decomposes before it melts or vitrifies. Its porous characteristic makes a finished ferrite element susceptible to moisture-caused destruction under the usual operating conditions.

This has been overcome in the past by the extra step of coating the finished ferrite element with a'vitreous material such as glass. Such a coating had the advantages of hermetically sealing the surface of the ferrite body, while at the same time improving the impedance match between the ferrite and space, or vacuum, since the glass has a dielectric constant approximately midway between that of ferrite and that of air or vacuum. This second step of vitreously coating the ferrite element required further equipment and added to the expense of making the dielectric element.

It is an object of the present invention to provide an improved ferrite element.

It is a further object to provide a method of manufacture of such an element which does not require extruding equipment.

It is another object to provide a method of manufacture which does not require coating of the ferrite element with glass.

It is still another object to provide a method of manufacturing a glass-impregnated ferrite element having a predetermined ferrite-glass distribution throughout its structure.

Briefly, in accordance with the present invention, these objects are achieved in the following manner:

Ferrite powders and a matching glass in powder form, both suspended in suitable media, are introduced and mixed in a predetermined proportion in a mold of predetermined shape and dimension and then thermally fused after removing the suspending media, thereby providing a glass-impregnated ferrite body having the shape of the mold. Instead of glass, any suitable glass-like or vitreous substance, such as quartz powder may be used for manufacturing the ferrite body of the invention.

The novel features which are believed to be characteristic of the invention, both as to its organization and by the rod extrusion process and may seriously weaken the ferrite element against thermal strains when in use. Further, the shape of the ferrite element is limited by certain grinding processes in view of the fragility of the ferrite rod.

Referring to Fig. 2, there is shown an example of apparatus used in the'process in accordance with the present invention. Carbon mold 16 is provided with an inner recess 18. Obviously, recess 18 may be any desired shape. Neck portion 20 is a channel connecting recess 18 to a feeding nozzle 22. A pair of conduits 24 and 26 I convey, respectively, the suspension of ferrite powders stantially at 28 and 30 heat the mold in such a manner that the glass and ferrite will be fused. Supersonic vibrator indicated substantially at 32 is shown in acoustical connection with mold 16 for tamping or packing more densely the ferrite and the glass in recess 18. Circular grains 24' represent the powdered glass granules and triangular grains 26' represent the ferrite powder granules.

Referring to Fig. 3, there is shown an alternative example of apparatus suitable in the process of the invention. Plaster casting mold 15 is formed to provide a recess 17 which may be of any desired predetermined shape and size corresponding to that of the ferrite element. Feeding nozzle 21 is connected to recess 17 through a neck portion 19. Beakers 25 and 27 contain, respectively, a ferrite casting slip and a glass powder suspension and are shown as examples of means for introducing and programming the introduction of these materials into recess 17. Beakers 25 and 27 pour into a mixer 23 which stirs the two slurries into one homogeneous slip, then pours the one combined slip into nozzle 21 and thence into neck portion 19 and finally into recess 17 wherethe casting slip may be settled by ultrasonic vibrator 32 and dried by plaster cast 15 which absorbs the liquid of the slurry. When the cast slip has been dried, the ferrite element is heated by heating elements 28 and 30 to fuse the ferrite and glass.

The manner of preparation of suitable slips is well known in the ceramic art; a general discussion of techniques and theories of casting slips is given in Elements of Ceramics (Addison-Wesley Press, Cambridge, Mass, 1952), by F. H. Norton, chapter 10.

Fig. 4 illustrates a finished ferrite element 34; neck portion 35' shown in dotted lines may .be removed.

Referring-to Fig. 5,,graph .36 plots-the percentage of glass in the-composition ofthe ferrite .element as a function of :position along the length of the ferrite element. Graph 38 in like *manner shows the percentage composition of ferrite as the function of position along the length of the ferrite element.

In practicing the process ofthe present invention, as illustrated by Fig. 2, ferrite and glass powder, .as represented by;grains24"and;glass grains 26., is fed in liquid suspension through conduits 24 .and 26, respectively, by appropriate pressure or,gravity feed through nozzle 22, into mold 16, and :via neck portion into recess 18. The flow of :the powders may be programmed in such a manner that, as shown by curves 36 and 38, the ends-of the finished element maybe substantially of glass while the intermediate portion is substantially of ferrite with, however, enough glass impregnated in the ferrite to hermetically seal and bond the ferrite. Impedance mismatch for microwaves propagated from air or vacuum into and along the length of the ferrite element is in this manner substantially eliminated because the end portion is not only tapered but is composed substantially of glass having a dielectric constant intermediate that of air and ferrite. Further, the dielectric constant is only gradually increased to that of ferrite becauseof the smooth transition of glass to ferrite proportion along the length of the ferrite element. Vibrator 32 operates to pack more densely the powders'or slurry by ultrasonic vibration of form 16. When the introduction .of the powders or slurry is completed, heating elementsZS and may be energized to fuse the glass and ferrite'into one ferrite ele ment. Then the heatersare' de-energized; form 16 cooled and open; and ferrite element 34 removed. Neck portion 35 may then be removed, and the.element.is ready for use.

In like manner, the method of the invention, as illustrated in Fig. 3, including the programming and introduction of ferrite and glass into casting recess 17 in plaster cast 15, is such that the composition of the finished ferrite element is that shown by the graphs of Fig. 5.

Therehas thus .been disclosed a processfor manufacturing a glass-impregnated ferrite element having an arbitrary percentage gcomposition .of :glass and ferrite along its length whichis impervious tomoisture, is hermetically sealed, andhas an improved impedance match between the ferrite dielectric and space. Further, there has been disclosed a process which requires neither the use of extruding equipment nor the addedstep of glass coating a fragile extrudedqferrite element.

Whatis claimed is:

l. A method for making a ferrite element suitable'for use in microwave devicesand being impregnated with a vitreous material whereby the ferrite element is bonded and hermetically sealed, the method providing a proportional composition of ferrite versus vitreous material which varies smoothly-along the direction from end to end of said element,.said composition being substantially of vitreous material near said ends of said element and predominantly ferrite at an intermediate portion between said ends and having'a continuous transition between said ends andtsaid intermediate portion for improved impedance 'match between said ferrite and space, said methodcomprising: simultaneously pouring'a stream of ferrite powderand a stream'of vitreous powder in suitable form together into a tapered mold; varying the relative rnent; compacting the rate of pouring of said streams in accordance with a definite program so as to produce said element having said proportional composition; compacting said powders in said mold; of substantially vitreous material near said ends and predominantly ferrite at an intermediate portion providing sufficient vitreous material throughout to bond and hermetically seal said element and thermally fusing said ferrite and glass powders into the desired ferrite element.

2. A method for making an elongatedferrite element having tapering ends and suitable for use in microwave devices and being impregnated with a vitreous material whereby the ferrite element is bonded and hermetically sealed, the method providing a proportional composition of ferrite versus glass which varies smoothly and continuously along the direction from end to end of said elongated element, said composition being substantially of glass material near said ends of said element and of predominantly ferrite at an intermediate portion between said ends and having a continuous transition between said endsand said intermediate portion for improved impedance matching between said ferrite and space, said method comprising: simultaneously pouring two casting slip streams of, respectively, ferrite and glass powder suspensions into a tapered, elongated mold; varying the relative rate of pouring of said streams in accordance with a definite program so as to producesaid varying proportional composition of substantially glass material near said ends and predominantly ferrite at an intermediate portion providing, however, sufiicient glass throughout to bond and hermetically seal said eleferrite and glass suspensions; and thermally fusing said ferrite and glass suspension into the desired ferrite element.

3. A method for making an elongated ferrite element having tapered ends and suitable for use in microwave devices and being impregnated with glass whereby the ferrite element is bonded and hermetically sealed, the method providing a proportional composition of ferrite versus glass which composition varies smoothly along the direction from end to end of said elongated element, said composition being substantially glass near said ends of said element and predominantly ferrite at anintermediate portion between said ends andhaving a continuous transition of proportional composition between said .ends and said intermediate portion for improved impedance matching between said ferrite and space, said method comprising: simultaneously pouring two powder streams of ferrite and glass powders, respectively, into a tapered mold; varying the relative rate of pouring of said stream in accordance with adefinite program :so as to produce said element having said proportional composition of substantially glass near .said ends and predominantly ferrite at an intermediate portion therebe tween providing, however, sufiicient glass throughout said elongated element to bond and hermetically seal it; compacting said' powders in said mold; and thermally fusing said granular ferrite and glass into the desired ferrite element.

References Cited in the file'of this-patent UNITED STATES PATENTS 1,336,740 Gerber .Apr. 13,1920 1,929,425 Hermann c Oct. .10, 1933 2,196,253 ,Erdle ,-Apr., 9, ,1940 FOREIGN PATENTS 168,261 Great Britain Sept. 1,1921 683,722 Great Britain Dec.,.3,11952 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,930 O97 March 29, 1960 Arthur H. Iver-sen It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 3 and 4, strike out compacting said powders in said mold;" and insert the same after "element" in line 7,

same column.

Signed and sealed this' 11th day of October 1960.

(SEAL) Attest:

EARL H. AXLINE A'tfiesting Ofiicer ROBERT C. WATSON Commissioner of Patents 

1. A METHOD FOR MAKING A FERRITE ELEMENT SUITABLE FOR USE IN MICROWAVE DEVICES AND BEING IMPREGNATED WITH A VITREOUS MATERIAL WHEREBY THE FERRITE ELEMENT IS BONDED AND HERMETICALLY SEALED, THE METHOD PROVIDING A PROPORTIONAL COMPOSITION OF FERRITE VERSUS VITREOUS MATERIAL WHICH VARIES SMOOTHLY ALONG THE DIRECTION FROM END TO END OF SAID ELEMENT, SAID COMPOSITION BEING SUBSTANTIALLY OF VITREOUS MATERIAL NEAR SAID ENDS OF SAID ELEMENT AND PREDOMINANTLY FERRITE AT AN INTERMEDIATE PORTION BETWEEN SAID ENDS AND HAVING A CONTINOUS TRANSITION BETWEEN SAID ENDS AND SAID INTERMEDIATE PORTION FOR IMPROVED IMPEDANCE MATCH BETWEEN SAID FERRITE AND SPACE, SAID METHOD COMPRISING: SIMULTANEOUSLY POURING A STREAM OF FERRITE POWDER AND A STREAM OF VITREOUS POWDER IN SUITABLE FORM TOGETHER INTO A TAPERED MOLD, VARYING THE RELATIVE RATE OF POURING OF SAID STREAMS IN ACCORDANCE WITH A 